The invention relates to a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engines, particularly in a common rail injection system. A drive shaft is supported in a pump housing and is embodied as eccentric or has a number of cam-like projections in the circumference direction. Preferably the pump includes a number of pistons that are disposed radially with regard to the drive shaft, each in a respective cylinder chamber. Each piston can be set into a reciprocating motion in the radial direction in the cylinder chamber upon rotation of the drive shaft. Each piston is provided with a check valve on the intake side and on the high-pressure side, wherein for each piston, a metallic housing part, which constitutes the respective cylinder chamber, is provided with a fuel inlet opening and a fuel outlet opening.
In radial piston pumps of this kind, the housing part is supported and sealed in relation to other housing regions by a number of elastomer sealing elements. This leads to an indefinite arrangement of the components of the pump.
Based on this, an object of the current invention is to produce a radial piston pump that pumps a high pressure up to 2000 bar, in which the high-pressure-affected components and their sealing points uncoupled from each other and in the assembled state, are exactly defined statically.
This object is attained with a radial piston pump of the type described at the beginning, by virtue of the fact that the housing part rests with a flat contact surface against a flat contact surface of the metallic housing base body from the radial outside with regard to the drive shaft. A projecting section of the housing part, which is concentric to the cylinder chamber and is oriented toward the drive shaft, extends through a radial opening of the housing base body in the direction toward the drive shaft. The fuel outlet opening discharges into the flat contact surface and is flush with another outlet opening in the housing base body, and that a metallic high-pressure sealing element is provided in a widened mouth region of the fuel outlet opening in the housing part and/or the other outlet opening that is flush with it in the housing base body. The housing part, with the interposition of the metallic high-pressure sealing element, is tightened against the housing base body by way of screws in such a way that the high-pressure side is sealed through the clamping of the high-pressure sealing element.
Whereas in the previously known radial piston pump, the high-pressure seal was also achieved by way of interposed elastomer sealing elements, and the assembly of the components adjoining the high-pressure sidexe2x80x94as mentioned at the beginningxe2x80x94included a flux of force over a number of components which led to a static indeterminacy. The invention proposes to produce the seal by way of the high-pressure sealing element and by virtue of the fact that the flat metallic contact surfaces of the respective radially outer housing part and the housing base body are tightened against each other. The housing part can rest in a statically defined manner against the housing base body by way of the flat contact surfaces. When the housing part is tightened against the housing base body, a so-called hard seal of the high-pressure side is produced by the metallic high-pressure sealing element, which connects the outlet opening in the housing part and the other outlet opening in the housing base body to each other so that they permit fuel to flow through and are sealed in relation to the outside.
The high-pressure-affected sealing points of metallic components that are tightened against each other could also be embodied without the interposition of additional high-pressure sealing elements. To this end, the surfaces of the metallic components that rest against each other in a sealed fashion could be machined, in particular lapped, in order to produce a desire flatness and surface roughness. Then a hard seal (metal against metal) can likewise be achieved by tightening the components against each other. If the lapping can only be carried out with difficulty or is altogether impossible because a relevant component has a protruding pin or the like, or if the processing step of the lapping needs to be eliminated, then a surface quality that is sufficient for producing a hard seal can also be produced by means of hard turning, i.e. metal-removing machining, after the heat hardening. If, however, in accordance with the current invention, a metallic high-pressure sealing element is used in the manner described, then the machining expense is much lower and the pump can therefore be manufactured in a more reasonably priced fashion. Furthermore, greater manufacturing tolerances in the housing part and in the housing base body are possible, without the occurrence of leaks.
According to a preferred embodiment of the invention, the high-pressure sealing element is a double-cone sealing element. The double cone sealing element is then preferably received in the widened mouth region of the fuel outlet opening in the housing part and/or in the housing base body in such a way that the circumference edges of the respective outlet opening rest in a sealed fashion against the conical surfaces of the double cone sealing element.
The widened mouth region can, for example, be provided in the form of a stepped bore in the housing base body or in the housing part. In this instance, the preferably right-angled step constitutes the above-mentioned circular edge, which can be placed against the conical sealing surface.
According to another embodiment of the invention, the high-pressure sealing element can be embodied as annular and can constitute a sealing cap.
It has further turned out to be advantageous if the high-pressure sealing element is embodied as essentially in the shape of a bushing and produces a hard seal with its end faces encompassing the high-pressure-carrying openings.
In a quite particularly advantageous improvement of the above-mentioned concept of the invention, the bushing-shaped high-pressure sealing element is embodied as resilient in the axial direction. This can be advantageously achieved by virtue of the fact that on its inner and/or outer surface, the bushing-shaped high-pressure sealing element has recesses that extend in the radial and the circumferential direction.
A particularly good and operationally reliable seal is achieved if an edged or bead-shaped circumferential projection is embodied on the end faces of the high-pressure sealing element. With bushing-shaped high-pressure sealing elements, this can be achieved, for example, by means of end faces that are slightly inclined in relation to the longitudinal direction, i.e. extend in a conical fashion.
In order to assure a correct assembly position, it has turned out to be advantageous that the protruding section of the housing part oriented toward the drive shaft forms a centering collar with which the housing part can be positioned in the radial opening of the housing base body.
In order to keep the unusable dead space in the compression stroke of the pump piston as small as possible and to thus increase the efficiency of the radial piston pump, it has turned out to be advantageous if the intake side check valve and the high-pressure side check valve are integrated into the respective housing part that constitutes the cylinder chamber.
The cylinder chamber could be embodied by a blind bore that extends radially outward in the housing part. In order to be able to machine the wall of the cylinder chamber in a suitable manner, e.g. to lap it, it has turned out to be advantageous, though, if the housing part has a through opening that extends radially in relation to the drive shaft, constitutes the cylinder chamber, and is sealed on the radial outside by a metallic sealing element that is screwed into the through opening.
In order to seal the through opening by means of the metallic sealing element, this element is advantageously tightened with its end face against an axial step in the through opening in such a way that a high-pressure-tight seal is achieved.
In another improvement of this concept of the invention, an edged or bead-shaped circumferential projection is embodied on the end face of the sealing element and this leads to a sealing, plastic deformation along the projection when the components are tightened against each other. The projection itself, however, is not deformed, but only produces the hard seal of the flat surfaces.
This seal, which is called the biting-edge technique, is not limited to the sealing of the radial through opening in the housing part that constitutes the cylinder chamber by means of the sealing element, but can also be used on other insertion parts, particularly parts that can be screwed in, e.g. the seal of an access opening to a check valve or a high-pressure fitting that can be screwed in.
Other features, details, and advantages of the invention ensue from the graphic representation of the subsequent description of a preferred embodiment of the radial piston pump according to the invention.